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Stabilization/solidification (S/S) processes were utilized to immobilize lead (Pb) and tungsten&#x0D;(W) in contaminated soils, the inclusion of W motivated by the use of the new W-based&#x0D;ammunition. Artificially contaminated soils were prepared by mixing either kaolinite or&#x0D;montmorillonite with 10% Pb and 1% W (all percentages by dry weight). Type I/II Portland&#x0D;cement (PC), silica fume cement (SFC) and cement kiln dust (CKD) were used as S/S agents.&#x0D;The S/S agents were added at 5, 10 and 15 % for a curing time of 1-, 7- and 28-days. The&#x0D;toxicity characteristic leaching procedure (TCLP) and synthetic precipitation leaching&#x0D;procedure (SPLP) were used to evaluate the effectiveness of the treatments. X-ray powder&#x0D;diffraction (XRPD) was used to investigate the crystalline mineral phases responsible for Pb&#x0D;and W immobilization. The TCLP results showed that regardless of clay type and stabilizing&#x0D;agents, the Pb concentrations decreased with increasing pozzolan content. PC and SFC&#x0D;exhibited similar performance depending on the particular sample (not consistent with soil&#x0D;type, dosage, and curing time). The most effective stabilizing agent on Pb leachability was PC&#x0D;despite SFC being silica-enriched which should have contributed to its greater immobilization&#x0D;of Pb. TCLP-W was immobilized below 1 mg l-1 in every case. The most effective stabilizing&#x0D;agent on the SPLP-Pb leachability was CKD, consistently demonstrating among the lowest&#x0D;concentrations for each soil type due to pH control. PC and SFC exhibited similar&#x0D;performance depending on the particular sample (not consistent with soil type, dosage, and&#x0D;curing time). The W concentrations in SPLP leachate were very low in most samples&#x0D;indicating that W could be immobilized upon S/S processes even though W solubility is very&#x0D;high at elevated pH conditions (662.9 mg l-1 at pH~11), and would remain immobilized under&#x0D;SPLP exposure conditions. The XRPD results revealed that the formation of lead silicate&#x0D;(Pb4SiO6), stolzite (PbWO4) and lead tungsten oxide (Pb0.29WO3) were strongly associated&#x0D;with the immobilization of Pb in the S/S matrix.

Stabilization/Solidification (S/S) Pb and W Contaminated Soils using Type I/II Portland Cement, Silica Fume Cement and Cement Kiln Dust